The present invention is directed to a mitral valve annuloplasty ring and a method for implanting a mitral valve annuloplasty ring to treat mitral insufficiency in a patient. Mitral insufficiency, also known as mitral regurgitation, is a common cardiac abnormality wherein the heart's mitral valve does not properly close.
In a normally functioning heart, oxygenated blood passes from the left atrium through the opened mitral valve and into the left ventricle when the left ventricle is in a relaxed state. When the left ventricle contracts, the blood is pushed out of the left ventricle thereby closing the mitral valve to prevent blood flowing back or regurgitating into the left atrium. From the left ventricle, the oxygenated blood is pumped out of the heart and directed to the rest of the body.
With mitral insufficiency, the mitral valve does not fully close and a portion of blood leaks back into the left atrium when the left ventricle contracts. As a result, the heart has to work harder by pumping not only its regular volume of blood, but also the extra volume of blood that regurgitates back into the left atrium. The added workload creates an undue strain on the left ventricle. This strain can eventually wear out the heart and result in death when the condition is prolonged and severe enough. Consequently, a properly functioning mitral valve is critical to the pumping efficiency of the heart.
Mitral valve annuloplasty is a well known approach for treating mitral insufficiency, although other treatments are used which include replacing the mitral valve, repairing the mitral valve leaflets, and shortening or replacing the chordae tendinae. Mitral valve annuloplasty is the reparation of the mitral valve annulus which effects full closure of the leaflets by reestablishing the size and shape of the normal mitral valve annulus. Such an annuloplasty most commonly incorporates the use of a mitral annuloplasty ring wherein the ring is implanted on the mitral valve annulus.
There are three basic types of mitral annuloplasty rings used in annuloplasty procedures. They include a rigid ring, a flexible ring and a combined ring that has both a flexible component and a rigid component.
Due to their inflexibility, the rigid rings dictate the shape and contour of the mitral valve. The native mitral valve annulus flexes in response to the movement of the heart. However, with a rigid ring the annulus is not able to flex normally or move freely with the pumping action of the heart. As a result of the rigidity, the physiologic factors that normally shape the mitral valve annulus are not allowed to take precedence in shaping the valve.
Another drawback with rigid rings is that they can induce a heart condition known as systolic anterior motion in patients having a mitral valve posterior leaflet that is too "tall". During ventricular contraction, the posterior leaflet pushes the anterior leaflet in a direction opposite to the anterior leaflet's normal movement, resulting in the obstruction of the left ventricle's outflow tract.
Overall, rigid annuloplasty rings do not allow the mitral valve annulus to reestablish its normal shape and form as dictated by the action of the heart pumping. The shape and contour of the annulus is established by the inflexible shape and form of the ring itself.
Flexible rings made of Dacron cloth, unlike the rigid rings, can allow the mitral valve annulus to move and flex as the heart contracts and relaxes. However, several drawbacks still exist. Proper shape and contour of the annulus is necessary in order for the mitral valve leaflets to close effectively. One shortcoming of the flexible ring is its predisposition to crimp during implantation. Crimping can be detrimental to the valve annulus, sometimes resulting in a mitral orifice that is too small. This can lead to stenosis of the valve. Furthermore, neither the flexible rings nor the combined rings will remain flexible indefinitely after annuloplasty. Since the rings are secured in place by a line of sutures attached directly to the annulus, scarring and resultant stiffening of the annulus inevitably develops. This loss of flexibility impedes the normal flexing and movement of the heart, particularly the left ventricle and, therefore, the heart cannot function optimally.